Translation regulation of integrons gene cassette expression by theattCsites

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Integron are genetic elements able to carry, capture and shuffle the genes embedded in gene cassettes. TheattCrecombination sites adopt a stable secondary structure when single-stranded that is necessary for their recombination. In this study, we evaluated the impact of the structure of theattCsite on expression of the 3′ gene in class 1 integrons. This was analysed by substituting theattCof theblaIMP-8 gene cassette with various mutatedattCsites spanning a wide range of sizes and secondary structures, and measuring the integron-dependent translation of the 3′aac(6′)-Ib7gene. In the resulting constructs, the 5′-attCsite differentially affected the expression of theaac(6′)-Ib7gene. Contrary to what was expected from their proposed role as Rho-independent transcription terminators, the transcription of theaac(6′)-Ib7gene was not affected by the variousattCsites. Mutations of natural sites revealed that destabilization of the potential stem-loop structure of theattCsite in the transcript could enhance the expression of the 3′ gene. In particular, the presence of a translated open reading frame was shown to increase translation of the 3′ gene. These findings might be explained by the capacity of the stem-loop structures to impede ribosome progression.

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